Measuring the effect of water vapor on climate warming

Mar 18, 2014

Water vapor is a potent greenhouse gas. In the atmosphere, the concentration of water vapor increases with the temperature, setting up a powerful positive feedback loop. This water vapor feedback is the strongest known positive feedback, with the potential to roughly double the effect of warming caused by other sources. Determining the exact strength of the water vapor feedback, then, is incredibly important to limiting uncertainty in future climate change projections.

From 2002 to 2009, an infrared sounder aboard NASA's Aqua satellite measured the atmospheric concentration of . Combined with a radiative transfer model, Gordon et al. used these observations to determine the strength of the water vapor feedback. According to their calculations, atmospheric water vapor amplifies warming by 2.2 plus or minus 0.4 watts per square meter per degree Celsius. This value, however, is only the "short-term" feedback—the strength of the feedback as measured during the observational period. This value is subject to short-term climate variability. The true value of the feedback, the "long-term" value, is what the short-term observed values should trend towards when given enough time.

Using a series of climate models, the authors estimate the strength of the long-term water vapor feedback. Extrapolating from their short-term observations they calculate a long-term feedback strength of 1.9 to 2.8 watts per square meter per degree Celsius. They find that most models get to within 15 percent of their long-term value within 25 years. The accuracy of calculations, then, could be improved with a longer set of observations.

Explore further: Water in stratosphere plays key role in Earth's climate

More information: An observationally based constraint on the water-vapor feedback, Journal of Geophysical Research-Atmospheres, DOI: 10.1002/2013JD020184, 2013 http://onlinelibrary.wiley.com/doi/10.1002/2013JD020184/abstract

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User comments : 19

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orti
2.8 / 5 (8) Mar 18, 2014
If more water vapor; then more clouds, more snow and ice, and a higher planetary albedo. Seems to me water also has a strong negative feedback.
Maggnus
3.9 / 5 (7) Mar 18, 2014
True, it's a feedback effect that is accounted for in the climate models.
cantdrive85
2.1 / 5 (13) Mar 18, 2014
True, it's a feedback effect that is accounted for in the climate models.

And we "know" those models are perfect and infallible.
shavera
4.2 / 5 (10) Mar 18, 2014
If you can publish a better one, please feel free. Or if you can demonstrate with solid evidence that the current models are so significantly off that their predictions (including error bounds) are completely incorrect, again, please feel free to publish it, and make all the moneys and fame for disproving AGW.

Until then, please leave your useless ranting off of internet message boards.
Zachia
2.4 / 5 (7) Mar 18, 2014
Water vapor is a potent greenhouse gas
This feedback can become negative easily. It depends on size of droplets and their altitude. White clouds reflect lotta energy, but these high-altitude ones are reflecting it back to surface instead.
Maggnus
4 / 5 (8) Mar 18, 2014
True, it's a feedback effect that is accounted for in the climate models.

And we "know" those models are perfect and infallible.

We do? Funny, I always thought they were just models, intended to give a picture of what can be expected, in general terms, given different scenarios.

Of course, we "know" those models have a better track record than, say, pseudo-scientific EU theory right? At least they are based on reality, unlike something ridiculously stupid like, oh say, EU, right?
orti
2.3 / 5 (10) Mar 18, 2014
Magnus: What's EU?
Shavera: That has been done by at least one climatologist with access to the best satellite data. And those IPCC models have been over predicting for at least the last decade and a half.
Maggnus
3.9 / 5 (7) Mar 18, 2014
Magnus: What's EU?
A quasi-religious pseudoscience called Electric Universe Theory.
And those IPCC models have been over predicting for at least the last decade and a half.
And even of that were true, which it actually isn't, the models considered by the IPCC were not just about surface temperature.
runrig
4.5 / 5 (8) Mar 19, 2014
If more water vapor; then more clouds, more snow and ice, and a higher planetary albedo. Seems to me water also has a strong negative feedback.


No, doesn't work like that. WV has a life span of around 10 days in the atmosphere - due the hydrological cycle (evap from surface > condensation to cloud in atmos > precip out of clouds) and so it's atmospheric concentration is self regulating.. Here they talk in absolute terms - ie more WV (atoms of H2O) but this will not create more clouds and hence increase albedo. It is the RELATIVE quantity of WV available that matters. Warming air can hold more molecules of water, yet its relative humidity remain constant. Clouds therefore are a relative constant also.
Tim Thompson
4.3 / 5 (7) Mar 21, 2014
The point of water feedback is this: The atmosphere is on average saturated. So if all you do is add water vapor, you get more rain, not more temperature. But if you add something like CO2 first, that will raise the temperature. The warmer air can hold more water, and gets even warmer because water is an even stronger greenhouse gas than CO2. But it saturates again quickly, and the warming stops. But if you keep adding CO2, then the process does not stop, and you get what we now call "global warming". As long as you keep adding CO2 (or something with the same IR radiative transfer properties), you keep warming.
ryggesogn2
1.5 / 5 (8) Mar 21, 2014
something with the same IR radiative transfer properties)

Like water vapor?
Water vapor has more IR absorption bands from 8-12 um than CO2.
rockwolf1000
3.4 / 5 (5) Mar 21, 2014
something with the same IR radiative transfer properties)

Like water vapor?
Water vapor has more IR absorption bands from 8-12 um than CO2.


Hey Rygg. Are you stupid or something?
Tim Thompson
4.3 / 5 (6) Mar 21, 2014
Like water vapor?

Like I said in the post you responded too …
The atmosphere is on average saturated. So if all you do is add water vapor, you get more rain, not more temperature.

cantdrive85
1.6 / 5 (7) Mar 21, 2014
We do? Funny, I always thought they were just models,

What's funny is fools like you insist we return to the dark ages based upon these models.
rockwolf1000
3.9 / 5 (7) Mar 21, 2014
We do? Funny, I always thought they were just models,

What's funny is fools like you insist we return to the dark ages based upon these models.


Indeed. Everyone knows the economy is way more important than food, water and air. Who needs to eat, drink or breathe when you can look at money all day?
ryggesogn2
2.1 / 5 (7) Mar 21, 2014
The military has an LWIR (8-12um) air to ground missile which has great range over dry desert conditions.
Over a humid region, the contrast is significantly reduced.
Could it be water vapor that significantly attenuates IR in the 8-12 um band?

he economy is way more important than food, water and air.


Are you stupid or something? Without a prospering economy there is NO food, water or clean air.
Socialists AGWites actions are destroying the economy.
rockwolf1000
3 / 5 (4) Mar 21, 2014
The military has an LWIR (8-12um) air to ground missile which has great range over dry desert conditions.
Over a humid region, the contrast is significantly reduced.
Could it be water vapor that significantly attenuates IR in the 8-12 um band?

he economy is way more important than food, water and air.


Are you stupid or something? Without a prospering economy there is NO food, water or clean air.
Socialists AGWites actions are destroying the economy.

Food, water and clean air have been around for a lot longer than our economy. The problem is our current economy is threatening our supplies of food water and clean air. That you can't recognize that speaks volumes about your level of understanding and comprehension or lack thereof.
If ever there was someone who deserved to have their voice silenced, their liberty denied and their wealth plundered, it most certainly would be you!
ryggesogn2
2.6 / 5 (5) Mar 23, 2014
Food, water and clean air have been around for a lot longer than our economy.

Without a market based economy there is no plentiful food, water or clean air.
Zimbabwe, Venezuela, USSR are but a few examples.
ryggesogn2
2.3 / 5 (6) Mar 23, 2014
"Panelist Curry thinks computer models place too much emphasis on current CO2 levels and not enough on long-term cycles in ocean temperature that have a huge influence on climate. She suspects we may be approaching a period similar to 1965-1975, when there was a clear cooling trend.

Climate is affected by an infinite number of variables, the relative importance — and complexity of their interactions — of which aren't fully understood.

Put too much weight on one and not enough on the other, and you have the computer phenomenon known as GIGO — garbage in, garbage out.

The American Physical Society hopes to take out the garbage. If it succeeds, climate alarmism and its mythical consensus, not the ice caps, will melt away.

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